This invention relates to the treatment of electronic components and the like and, more particularly, to a novel and highly effective lead tinning system which propels electronic components along a path where they receive various treatments such as fluxing, tinning (soldering), washing and drying.
Electronic components such as semiconductor devices must in many cases be given various treatments in order to render them suitable for movement in channels of trade and for their intended end uses.
One type of electronic component which is treated in this manner is known in the industry as a Dual In-Line Package (DIP). Such DIPs come in various sizes: the length, width and thickness of the plastic or ceramic rectangular body portion may all vary independently. A plurality of "legs" (leads or terminals) emerge from the sides of the body portion and are normally bent so that the legs on either side lie in a plane which is generally parallel to the side of the body portion from which the legs emerge and perpendicular to the top and bottom surfaces of the body portion.
As the DIPs are transported along a track through various treatment stations, they can be arranged so that the legs point down, in which case they are referred to as "live bugs", or up, in which case they are referred to as "dead bugs". The preferred arrangement may depend on the intended treatment.
Conventional apparatus for propelling such DIPs in the "live" position through various treatment stations is exemplified by the disclosure of a Japanese patent laying open No. 128051/1982. That documents discloses (A) a supply station, (B) a flux station, (C) a soldering station, and (D) a washing and drying station, together with a lower rail and a pair of upper guide members which extend from one station to another to facilitate movement of the DIPs. The purpose of the upper guide members is to keep the DIPs from falling off the lower rail as they move along the rail and receive various treatments. The lower rail has different shapes in the several stations, depending on the nature of the treatment effected at each station. The upper guide members have the form of a pair of spaced-apart wire-like bars engageable with the top of the DIPs in stations (A), (B) and (D); and they have the form of a pair of spaced-apart bars of L-shaped cross-section engageable each with the top and one side of the DIPs in station (C).
Feed pins are arranged at regular intervals for propelling groups of DIPs along the lower rail through the various treatment stations. The feed pins are attached to an endless conveyor and extend vertically downward between the pair of upper guide members in order to engage and propel the DIPs.
There are some serious drawbacks to this conventional apparatus. First, as indicated above, DIPs come in different thicknesses. While all of the DIPs receiving treatment in a given run are likely to be of the same thickness, the DIPs treated in successive runs may vary greatly in thickness. The conventional apparatus described above cannot easily be modified or adapted to handle DIPs of different thickness.
In particular, there is no easy way to adjust the separation between the upper guide members and the lower rail. This is a serious problem, since any attempt to treat DIPs of substantially increased thickness will tend to cause binding of the DIPs between the upper guide members (even if they have some flexibility) and the lower rail; and any attempt to treat DIPs of substantially reduced thickness will deprive the DIPs of the restraint intended to be imposed by the upper guide members and will therefore result in DIPs becoming dislodged from the lower rail as a result of encountering a standing wave in the solder pot, a blast of air in the drying section, etc.
Moreover, even if the prior apparatus were somehow modified to permit easy adjustment of the separation between the upper guide members and the lower rail, the apparatus would be less than satisfactory, because the vertically-extending feed pins must either be excessively long, in order to be engageable with DIPs of all thicknesses, or be positionally adjustable in a vertical direction. The latter type of adjustment is unduly complicated, especially since the pins are mounted on a movable endless conveyor.
Another drawback of conventional apparatus stems from the fact that DIPs come in different widths. The conventional apparatus described above cannot easily be modified or adapted to handle DIPs of different widths.
It is important that the width of the lower rail be reasonably related to the width of the DIPs transported on the rail. If the DIPs are narrower than the rail, and it is desired to propel them along the rail in the "live" position (for example, in order to tin the legs), the legs will not fit over the rail, and the process becomes unworkable.
On the other hand, if the DIPs are too much wider than the rail, they can slip sideways or become cocked on the rail to the point where they are unacceptably positioned for purposes of correct treatment, or even slip sideways to the point where they topple off the rail.
In the conventional apparatus, access to the lower rail for the purpose of replacing it with another rail of different width is awkward, since no provision is made for conveniently displacing the upper guide members. In the absence of such provision, it is necessary to custom-build the apparatus to accommodate each size of component or to resort to partial disassembly of the apparatus merely in order to have access to the lower rail. This is expensive in terms not only of the direct labor involved but also of the production lost because of downtime of the apparatus.